There’s a mismatch between what science suggests and what schools do on this.

A century of scientific study converges on a key insight for our design of curriculum and assessment: an insight that can be put work immediately, widely, at no cost, and to great effect.

In the scientific literature there are hundreds (if not thousands!) of studies on this, some from as early as 1907, and the research in the last decade is particularly prolific:

In 2013, five cognitive scientists (Dunlosky, Rawson, Marsh, Nathan, Willingham 2013) collated hundreds such studies and showed that practice testing has a higher utility for retention and learning than other techniques: